Opaque Growth Zones Research Articles

Age and growth of narrow-barred Spanish mackerel Scomberomorus commerson in the coastal waters of southern Mozambique and KwaZulu-Natal, South Africa

The narrow-barred Spanish mackerel Scomberomorus commerson is one of the most important linefish species caught in KwaZulu-Natal and southern Mozambique waters, forming the basis of important commercial, artisanal and recreational fisheries. A total of 439 S. commerson were sampled along the east coast of southern Africa (KwaZulu-Natal, South Africa, and southern Mozambique) between April 2011 and March 2012. Retrospective length-at-age data observed from whole otoliths were used to compare and describe sex-specific growth. Growth rates obtained from otolith-derived data were compared with those estimated from 29 tag-recaptured fish. Overall, ages ranged from 0.48 to 14.6 years for females and 0.4 to 13.57 years for males. Otolith readings yielded an average percent error of 11.21%, lower than recorded in a previous study from the region. Marginal zone analysis provided strong evidence that one translucent and one opaque growth zone were laid down annually. Schnute growth-function parameters indicated significant differences in growth between sexes. Females approached their mean asymptotic length at a faster rate, and grew to a greater mean length-at-age, relative to males. Growth in both sexes was rapid, achieving 67.46 cm FL (females) and 65.4 cm FL (males) in their first year of life. Growth rates obtained from tag-recaptured S. commerson indicated slower growth for smaller/younger fish up until 70 cm FL after which growth was very similar to that observed from otolith-derived data. The results of this study provide accurate, validated life-history parameters for king mackerel that are important for the assessment of stock status in the region.

Spatial variation in demography of an estuarine teleost: implications for population and fishery assessments

Length- and age-based information is used to assess the exploitation status of har- vested populations of fish worldwide. This study examined variability in length-at-age, length and age compositions and derived demographic parameters of Acanthopagrus australis (Sparidae) captured in beach seines in 3 estuaries across 5 yr. The method of ageing fish by counting opaque growth zones on sagittal otoliths was validated by field and aquaria studies. Length-at-age rela- tionships varied according to gender, age class and estuary. Females older than 3 yr had a signif- icantly greater mean length-at-age than males, and this was consistent across all estuaries. For both genders, mean length-at-age of fish older than 4 yr was greatest in the southernmost estuary, and least in the northernmost estuary, suggesting differential growth dynamics among estuaries. Observed longevity differed among estuaries, ranging from 14 to 22 yr. Variations in length com- position of retained catches were subtler than those for age composition. The average age of fish in catches varied among estuaries from 4.2�5.1 yr to 6.8�8.2 yr even though fish within 5 cm of the minimum legal length dominated catches in all estuaries. Estimates of total and fishing mortality varied 3-fold among estuaries, with fishing mortality exceeding natural mortality. Variability in demographic characteristics was generally greater among estuaries than among years within each estuary. These results show that the population demographics and ensuing assessments should not be extrapolated across estuaries or from one estuary to the entire A. australis population. Length is a poor predictor of age and future sampling of populations must be age-based and strat- ified to account for estuary-specific variation in demography. Failure to account for such varia - bility could confound assessments and management deliberations necessary for determining the most appropriate harvest and conservation strategies for such species.

Age estimation and validation for South Pacific albacore Thunnus alalunga

Validated estimates of age are presented for albacore Thunnus alalunga, sampled from a large part of the south-western Pacific Ocean, based on counts of annual opaque growth zones from transverse sections of otoliths. Counts of daily increments were used to estimate the location of the first opaque growth zone, which was completed before the first assumed birthday. The periodicity of opaque zones was estimated by marginal increment analysis and an oxytetracycline mark-recapture experiment. Both validation methods indicated that opaque zones formed over the austral summer and were completed by autumn to winter (April to August). The direct comparison of age estimates obtained from otoliths and dorsal-fin spines of the same fish indicated bias, which was assumed to be due to poor increment clarity and resorption of early growth zones in spines, resulting in imprecise age estimates. As such, age estimates from otoliths are considered to be more accurate than those from spines for T. alalunga. This is consistent with results for a growing number of tropical and temperate tuna Thunnini species. It is recommend that validated counts of annual growth zones from sectioned otoliths is used as the preferred method for estimating age-based parameters for assessment and management advice for these important stocks.

Validation of annual periodicity in otoliths of red snapper, Lutjanus campechanus

The periodicity of otolith growth increments (opaque and translucent zones) from adult red snapper (Lutjanus campechanus) was examined through a mark and recapture study (2005–2010), and laboratory holding of hatchery reared red snapper over a 2 year period (2002–2004). Wild red snapper (n = 295) were caught hook-and-line, marked with anchor tags, injected with oxytetracycline dihydrate (OTC), and released in the Gulf of Mexico 15–40 km south of Dauphin Island, Alabama. Marked fish were recaptured up to 2.8 years after release (n = 35) and sagittal otoliths were dissected, sectioned and examined under white and blue-violet light. The number of opaque growth zones past the OTC mark was compared to time at liberty for each fish and supported an annual periodicity of growth increment formation. Also, most (87%) of the hatchery reared fish showed two opaque zones that supported an annual increment formation rate. However, an unusual timing of opaque zone formation was shown for mark-recaptured fish. Based on known timing of OTC marking, otoliths from mark-recapture fish showed opaque zone formation from late summer (August) to early winter (December). This fall formation of opaque zones is in contrast to previous studies and its timing may relate to the end of spawning for this species.

Age validation and variation in growth, mortality and population structure of Liza argentea and Myxus elongatus (Mugilidae) in two temperate Australian estuaries

This study investigated variation in the rates of growth and mortality, and age and fork-length (L(F)) compositions of two exploited species of Mugilidae, Liza argentea and Myxus elongatus, in two south-east Australian estuaries (Lake Macquarie and St Georges Basin). An ageing protocol was developed by counting opaque growth zones on sectioned otoliths which was validated by periodically examining the otoliths of captive-reared young-of-the-year fishes, and marginal increment analysis of wild fishes. The maximum recorded age was 17 years for L. argentea and 12 years for M. elongatus, which is greater than generally observed in other species of mugilids. Growth models of each species significantly differed between sexes and, except for male L. argentea, between estuaries. Fishes from Lake Macquarie generally had a greater mean L(F) at age than those from St Georges Basin and females of both species generally attained a greater maximum L(F) and age than males. Gillnet catches of L. argentea were of similar L(F) and age compositions in both estuaries, whereas the age composition of catches of M. elongatus in Lake Macquarie contained a greater proportion of younger fish. Estimates of total, natural and fishing mortality were greater for M. elongatus than L. argentea across both estuaries, and estimates of total mortality were greatest for both species in Lake Macquarie. The data indicate that neither species has been overfished in these estuaries.

Age and Growth of Spotted Sand Bass, Paralabrax maculatofasciatus, in Bahia de Los Angeles, Baja California, Mexico, with Age Validation using Otolith Edge Analysis

Spotted sand bass, Paralabrax maculatofasciatus, were collected from Bahia de Los Angeles, Baja California, Mexico covering as wide a size range as possible over four seasons (spring, summer, fall, and winter). Age was estimated and growth parameters calculated from growth zones counted in transverse otolith sections. An otolith edge analysis indicated an opaque growth zone was deposited once per year during the summer, validating the annual periodicity. Spotted sand bass from this region are fast growing with a relatively short life span of up to 11 years. Growth differs from the disjunct Pacific coast population by having a higher growth rate and a shorter longevity.

Age and growth of two endemic flatfish (Colistium guntheri and C. nudipinnis) in central New Zealand waters

Brill (Colistium guntheri) and turbot (C. nudipinnis) were aged by counting opaque growth zones in whole and sectioned otoliths. Zones counts from whole otoliths under-estimated age compared with counts from thin otolith sections. Other species of flatfish that have previously been aged from whole otoliths should be re-examined for evidence of age under-estimation, which may be common in species with thick otoliths. Marginal analysis of thin sections supported the hypothesis that one translucent and one opaque zone are formed each year in brill aged 5–10-years old. Marginal analyses for brill greater than 10 years of age, and for turbot, were inconclusive. However, 2+ and 3+ captive-reared turbot deposited the expected number of opaque zones from hatching. Both species grow rapidly for the first three years of life before growth slows appreciably. Turbot grow faster and larger than brill, and females grow faster and larger than males in both species. Growth is minimal in fish older than five years. Maximum observed ages were 21 years for brill and 16 years for turbot.

Age and Growth of the Leopard Grouper, Mycteroperca rosacea, in the Southern Gulf of California, Mexico

Growth of the leopard grouper, Mycteroperca rosacea (Streets, 1877), was analyzed in its natural habitat. Age determination was based on the reading of otoliths, and the method was validated under three main criteria: (1) pro-portionality, (2) seasonality, and (3) concordance with another method. Otolith growth is proportional to organism growth, with a slight degree of allometry, and the otolith registers the growth of the individual, even at advanced ages. The opaque growth zone in the otolith is deposited once a year, between July and October. Thus, taken together, one opaque and one hyaline mark represent an annual cycle. Back-calculated lengths-at-age agreed reasonably well with observed lengths-at-age at the time of capture, considering that back-calculated lengths represent an exact age (birthday), and observed lengths are taken at an intermediate age between birthdays. Fish length and otolith age data were fitted to the von Bertalanffy growth function by two methods: (1) linear regression (Ford-Walford and Beverton), using transformed data, and (2) nonlinear regression, by iteration. Although the nonlinear regression gave a fit with unbiased error, parameters resulting from linear regressions had a better biological meaning for the species. The resulting parameters were compared with those reported for other species of the family Serranidae.

Concentrations of strontium in the pectoral fin rays of the white sturgeon (Acipenser transmontanus) by laser ablation sampling - inductively coupled plasma - mass spectrometry as an indicator of marine migrations

Laser ablation sampling - inductively coupled plasma - mass spectrometry (LAS-ICP-MS) was an effective technique for the comparison of relative Sr concentrations in the opaque growth zones (annuli) in the fin rays of white sturgeon (Acipenser transmontanus). Three of 29 Fraser River white sturgeon (10.3% of the sample) showed significantly higher Sr fin ray concentrations in at least one annulus compared with the remainder of the fin ray, and this was interpreted as evidence of marine migrations. Eleven other individual fish had significantly higher mean Sr concentrations in their first 15 annuli compared with annuli 16-30 but lower than the concentrations of the three putative diadromous fish, and this was interpreted as evidence of time spent in the estuary. Eight Fraser River fish greater than 15 years old showed no significant increase in fin ray Sr concentations in the first 15 annuli, and Sr concentrations remained below 350 ppm throughout their lives. These individuals were considered likely to have spent most of their lives in a freshwater environment. Based on the evidence in this study, it is probable that the majority of white sturgeon in the lower Fraser River are not diadromous, but many spend extended periods of time in the Fraser River estuary as juveniles.

An Examination of Elemental Stability in the Fin Ray of the White Sturgeon with Laser Ablation Sampling–Inductively Coupled Plasma–Mass Spectrometry (LAS-ICP-MS)

Laser ablation sampling–inductively coupled plasma–mass spectrometry (LAS-ICP-MS) was used to examine the elemental composition of the opaque growth zones in the leading ray from the pectoral fin of 10 white sturgeon Acipenser transmontanus recaptured from the Columbia River. Changes in the elemental composition were detected within 2 years after their initial capture, with significant correlations among the concentrations of Sr, Mg, Pb, Br, Zn, Ba, Sn, Mn, and Na in the fin rays between the two capture periods. Concentrations of K suggested that fin ray material had been resorbed between captures and that the entire fin ray may be available for resorption. The cause of the changes in elemental composition of the fin rays was not determined. For this reason the use of fin rays from white sturgeon as biomonitoring structures must account for any resorption of the fin ray with time.

ニギス<i>Argentina semifasciata</i> K<sub>ISHINOUYE</sub>の年令及び成長に就て

The life history of the argentine, one of the most important fish of the deep-sea drag-net fishery, is little known yet. The present writer deals with the age and growth of the fish. Having examined the specimens taken from either Kumano-Nada, a well exploited ground, or off Kii-Suido, an almost untouched ground, he obtained the following results. 1) Left-side and right-side otoliths are symmetrical in every detail. 2) The 1st ring or clear band in the otolith is formed rather regularly in winter, while the 2nd ring formation in the same season is apparently not quite regular; the opaque growth zone outside the 2nd ring is usually indistinct. 3) The diameters of the 1st and 2nd rings are 2-5mm and 5-6mm respectively and their ranges hardly overlap each other. 4) Sometimes a pseudo-ring is formed, but it can be distinguished by its weak formation and its diameter. 5) By virtue of the above facts age determination by otolith is possible and growth can be traced. Argentine grows rapidly for several months after hatching, followed by later slower growth, and attains 130-150mm by the end of the 1st year, and 170-190mm by the end of the 2nd year. Since those fish which have more than one ring are few, it may be probable that the life span of the argentine is chiefly between one and two years.